CEDAR: Radar and Optical Observations of Enhanced Ion Acoustic Lines and Associated Auroral Fine Structure

Southwest Research Institute, San Antonio TX

Investigators

Abstract

The scientific objective of this project is to combine radar, optical and satellite data to investigate and characterize the occurrence of Naturally Enhanced Ion Acoustic Lines (NEIALs) with coincident auroral fine structures and to provide insight to their possible generation mechanisms. To accomplish this goal, the project will make use of common-volume observations of the nighttime auroral ionosphere with ground-based imagers and the Poker Flat Incoherent Scatter Radar (PFISR). In situ measurements will be made by the Japanese Reimei satellite which will pass once per night, near magnetic midnight, within the all-sky camera field of view (FOV). The observations will take place during the three moon down periods in early 2009 (mid-January through early-April), and one of the moon down periods in early 2010. PFISR observations of NEIALs have raised new questions regarding their occurrence in relation to specific auroral forms. The enhanced returns were found to occur in the dark regions immediately adjacent to thin auroral arc structures and to have altitude propagation at or near the Alfven speed. They are also found to occur near the poleward edge of the large-scale auroral features. Recent observations have found NEIALs to be associated with very dynamic, small-scale auroral arcs, indicative of Alfvenically accelerated electron precipitation. NEIALs in the PFISR data are observed with matching morphology and overlapping parameters as are the broad-band extremely low-frequency (BBELF) waves that are seen with satellites and rockets. These observations suggest connections between NEIALs and BBELF and Alfven waves. The understanding of NEIAL generation mechanisms is a beneficial addition to the incoherent scatter radar community, partly because the presence of NEIALs prevents the application of the normal fitting procedure used to derive the plasma parameters from the radar spectra. Also, NEIALs can be used as a means to study processes occurring in the ionosphere that would not otherwise be obtainable from ISR data. If NEIALs can be linked to specific types of wave activity, instabilities, or electron distributions, then ISRs provide a ground-based method to study when and where they occur.